Metastable Helium Is Changing The Way Scientists Look At Exoplanets [Infographic]

Recently, a team of scientists was able to detect metastable helium in the upper atmosphere of an exoplanet. This was quite an accomplishment considering it had never been done before. The formation of metastable helium in large amounts on exoplanets was theorized a long time ago but up until now, it had never actually been detected. This discovery marks a milestone in the study of exoplanet atmospheres as it will enable scientists to study planets that are much further away than the ones we are currently looking at.

Metastable helium was detected on a planet called WASP-107b. This planet has a large amount of helium in its atmosphere. So much in fact that it has been estimated that it stretches out tens of thousands of miles into space. The helium in the upper atmosphere is being bombarded with high-energy radiation from the host star’s chromosphere. That radiation ionizes the helium by knocking out one of the two electrons in each atom. These helium ions then combine with free electrons in the planet's atmosphere and often the new electron gets stuck in a high energy state. Having an electron stuck in this state is what makes a helium atom a metastable helium atom.

Getting an electron stuck in this state is related to a property that electrons have that is known as spin. If two electrons have their spin aligned then they cannot be at the same energy level. So when these helium ions pick up new electrons from the atmosphere they get stuck at a high energy level because the old electron is at a low level and the atoms will often pick up electrons with the same spin.

This creates the longest-lived excited state of any atom as the electron stays excited for about 2.2 hours on average. That is a long time considering that normally electrons de-excite in nanoseconds.

While in this excited state the electron can absorb a photon of infrared light and when it does it jumps to a slightly higher energy level. Afterward, it falls back down to the metastable state after a few nanoseconds. Once it does it can absorb another photon. This process goes on and on for the 2.2 hours that the atom is in the metastable state and then the atom falls back down to the regular ground helium state. Scientists are able to study this phenomenon by observing infrared light absorption.